1. Field of the Invention
The present invention relates to a semiconductor memory having a function of converting data supplied from outside into different data.
2. Description of the Related Art
In order to prevent unauthorized access to data, it is important to convert original data to different data by encoding or the like. In a security system which needs encoding of data, data encoded and stored in a semiconductor memory is read by being decoded. Generally, encoding and decoding are performed by a controller which accesses the semiconductor memory. More specifically, encoding and decoding are performed by software or hardware formed in the controller (See Japanese Unexamined Patent Application Publication No. 2005-78459, for example).
In a conventional security system, encoding and decoding are performed by a controller such as a CPU. The controller encodes data and writes the encoded data into a semiconductor memory. The controller reads the encoded data from the semiconductor memory and decodes the read data into the original data. Alternatively, the controller transfers the encoded data stored in the semiconductor memory to a hard disk drive or the like without decoding it. As just described, only the encoded data is inputted to and outputted from the semiconductor memory.
Generally, shifting a function of the controller to an external device can reduce the load on the controller, improving the performance of a system. However, there has been no semiconductor memory having an encoding function and a decoding function proposed.
For realizing the encoding function and the decoding function within the semiconductor memory, the semiconductor memory needs to input and output both unencoded data and encoded data. Specifically, data supplied from the controller to the semiconductor memory is not encoded. On the other hand, when encoded data in the semiconductor memory is transferred to a hard disk device or the like, the data outputted from the semiconductor memory is encoded. However, the operation technique and circuit technology of the semiconductor memory to deal with input and output of both of the encoded data and unencoded have not been studied. Moreover, the semiconductor memory may be accessed by plural controllers in the system. Hence, for the semiconductor memory having the encoding function and the decoding function, it is necessary to study a new control method for an access right.